The Study Of Occurrence Condition And Control On The Rice Downy Mildew (Sclerophthora Macrospora)

The rice downy mildew occurrence condirion, resistance between varieties, floodling in seedling bed and efficacy of fungicides control were studied in this thesis. The results provided:1. The rice could infected by downy mildew as early as in 4 leaf growing stage, after transplanted into paddy could also infcsted and the infection peak in tillering stage. 22 days after sowing, the plant infected rate was 1.8% , lday before transplant, the plant infected rate was 4.6% and 7 days after transplant, the plant infected rate was 9.7%, after that plant infected rate comes to stable;2. The resistance of rice to downy mildew had big difference between varieties, Weiyou 46 was the most sensitive variety, the disease index could be 10.92. Weiyou 644, Jinyou 207 and Peieryou 288 were the more sensitive varieties, the disease index were 7.07 6.44 and 5.62 Yuxiang 88,Y-You 1, II You 46 and Nongfuyou 1 were the resistance varities, the disease index were 0;3. The infested pressure mostly dependes on the seedling bed water tempreture.The trial results showed the disease index if seedling bed irrigated by reservoir water( 24℃) was higher, and if irrigated by lake water(28℃) was lower.4. The trial showed the efficacy of dimethomorph mancozeb on rice downy mildew was better than metalaxyl mancozeb. The efficacy of 69%dimethomorph mancozeb could be 71.39% at 800 dilution 3 times foliar spraying at 4 leaf stage, 1 day before transplant and tillering stage, respectively. The efficacy of 69%dimethomorph mancozeb could be 53.87% at 800 dilution 2 times foliar spraying at 4 leaf stage, 1 day before transplant without tillering stage, respectively. The efficacy of 69%dimethomorph mancozeb could only be 49.13% at 800 dilution if 1 treatment at tillering stage. The efficacy of metalaxyl mancozeb was 49.16% at 800 dilution 3 times foliar spraying at 4 leaf stage, 1 day before transplant and tillering stage, respectively.